The present invention relates to an image forming apparatus such as a printer, a facsimile or a copying machine.
In an image forming apparatus such as a copying machine or a printer, a sheet member (i.e., a sheet of paper) is supplied to an image forming unit from a sheet supplying tray disposed at a lower portion inside of the apparatus via a transportation path. The sheet supplying tray is adapted to previously contain therein the sheet member for use in image formation. In the sheet supplying tray are normally contained the standard-sized sheet members frequently used, on which an image is easily formed and which is favorably transported.
After the image formation in the image forming unit, the sheet member is discharged outside of the image forming apparatus. In recent years, the complexity of the image forming apparatus has increased and it is desirable that the image forming apparatus should have the functions of a copying machine, a printer, a facsimile and the like in combination, and that the sheet members to be discharged should be classified according to the image forming function, thereby obtaining an image forming system easy to be used. In order to achieve such an image forming system, for example, there has been proposed an image forming apparatus configured such that discharge ports, through which the sheet member in the image forming unit is discharged outside of the image forming apparatus via the transportation path, are disposed on both sides of the apparatus body, thereby facilitating the classification of the sheet members.
Furthermore, the image forming apparatus has been made to cope with space saving by reducing the size of the image forming apparatus or an area occupied for installation. Therefore, the transportation path in the image forming unit in the image forming apparatus is changed from a lateral orientation to a longitudinal orientation (i.e., a vertical direction). Thus, the number of image forming apparatuses having the transportation path of the longitudinal orientation has become increased in recent years.
In this manner, in the case where the transportation path in the image forming unit is oriented longitudinally, there can be configured a short transportation path for transporting the sheet member to the image forming unit from a sheet supplying device disposed at the lower portion in the image forming apparatus. Moreover, there is an advantage of efficient arrangement of the sheet supplying device, a sheet discharging tray unit for classifying the sheet members and stacking them thereon, a post-processing device and the like. To the contrary, since the transportation path is formed near a side surface, there is an inconvenience that an access must be made to the image forming apparatus not in front of the image forming apparatus but from the side surface thereof in the case where the sheet member is jammed on the transportation path.
Moreover, in the case where the transportation path in the image forming unit is oriented longitudinally, fixing means for fixing a developer onto the sheet member with the application of heat and pressure is disposed in the proximity of developing means for developing an electrostatic latent image formed on an image carrier or developer containing means for containing therein the developer (which is generally a toner) to be supplied to the developing means. Therefore, there is likely to cause a trouble that the developer having a melting property due to heat is melted and solidified.
Additionally, in the case where the transportation path in the image forming unit is oriented longitudinally, instability is caused since it is not determined as to whether the sheet member is tilted toward an obverse (i.e., toward the side of an image) or a reverse when the sheet member is transported from a transfer point of an image to be developed with the developer from an image carrier while a not-fixed developer image is carried thereon. As a consequence, the sheet member is unstably transported between a pair of fixing rollers in the fixing means. In addition, there is liable to arise a problem that the not-fixed developer image on the sheet member may be brought into contact with guide means or the like in the state of disorder during the transportation from the transfer point to the fixing means.
In order to solve the above-described problems, the longitudinally oriented transportation path is not a vertical transportation path, but there has been proposed a configuration in which a transportation path is slightly tilted in a direction in which the fixing means is separated from the developing means (that is, in a direction at the reverse of the sheet member, i.e., in a direction opposite to an image forming surface). With this configuration, since the transportation path is tilted, the sheet member passes the fixing means in the state in which the image forming surface is oriented upward.
In comparison with an image forming apparatus having the longitudinally oriented transportation path, which is disposed vertically, there arises a problem that it is difficult to release a cabinet disposed at a side surface and attach or detach a fixing device to or from the main body of the image forming apparatus at the time of maintenance or the like in an image forming apparatus having the above-described slantwise tilted transportation path.
Furthermore, in the case where the fixing device is heated since the image forming apparatus is in an energized state immediately before the maintenance or the like, the fixing device may be detached from the main body of the image forming apparatus when the fixing device stays at a high temperature. Consequently, for example, there has been proposed a configuration in which an abnormal increase in temperature at a grip can be prevented by disposing the grip, which is used in attaching or detaching the fixing device to or from the main body of the image forming apparatus, on a side opposite to heating means (see, for example, page 3, right lower column, lines 7 to 15 and FIGS. 1 and 2 in the specification of JP-A No. 4-179981).
However, as an image forming speed in the image forming apparatus is increased, the temperature at the pair of fixing rollers at the fixing device is liable to be decreased by the sheet member being transported. As a consequence, in the fixing device provided with the heating means only at a roller member of either one of the pair of fixing rollers, the temperature at the other roller member which is not provided with any heating means is extremely decreased, thereby causing fixing deficiency, so as to frequently interrupt an image forming operation.
In view of this, in the fixing device in the image forming apparatus in which the image forming speed is increased, it is general that both of the roller members constituting the pair of fixing rollers are provided with the heating means. In this case, since the temperature at the fixing device as a whole becomes considerably high, a fixing unit must be more carefully handled at the time of the maintenance or the like.
Although the outer wall of the fixing device is normally formed of a heat insulating member in order to keep the temperature to such an extent that there arises no problem even if a hand accidentally touches the outer wall of the fixing device, there is a danger of a burn if the fixing device may be strongly grasped. In particular, in the case where a serviceman or the like takes the fixing device out of the main body at the time of the maintenance, he or she performs the maintenance work after confirmation of the operation of the image forming apparatus. The fixing device is heated up to such a temperature as to fix an image formed on the sheet member immediately before the fixing device is taken out of the apparatus body. As a result, when the serviceman or the like takes the fixing device out of the main body, he or she must be sufficiently cautious.
However, in the case where the serviceman or the like awaits satisfactory heat dissipation from the fixing device while the fixing device remains disposed in the apparatus body until the temperature at the fixing device is decreased down to such a level that it is stable even if the fixing device can be firmly grasped by a hand, a long period of time is required since the fixing device is disposed inside of the apparatus body. Furthermore, operating efficiency is reduced, thereby raising a problem that a service time becomes prolonged in total.